Trimethylammonium-containing rhodacarborane [(9-NMe3-7,8-C2B9H10)RhCl2]2 as a catalyst for the annulation of arylcarboxylic acids with alkynes

Bis(Dicarbollide) Complexes of Transition Metals: How Substituents in Dicarbollide Ligands Affect the Geometry and Properties of the Complexes

The interaction between different types of substituents in dicarbollide ligands and their influence on the stabilization of various rotational conformers (rotamers) of transition metal bis(dicarbollide) complexes [3,3'-M(1,2-C2B9H11)2]- are considered. It has been shown that the formation of intramolecular CH···X hydrogen bonds between dicarbollide ligands is determined by the size of the proton acceptor atom X rather than its electronegativity. Due to the stabilization of rotamers with different dipole moments, intramolecular hydrogen bonds between ligands in transition metal bis(dicarbollide) complexes can have a significant impact on the biological properties of their derivatives. In the presence of external complexing metals, weak intramolecular CH···X hydrogen bonds can be broken to form stronger X->M donor-acceptor bonds. This process is accompanied by the mutual rotation of dicarbollide ligands and can be used in sensors and molecular switches based on transition metal bis(dicarbollide) complexes.

Triphenylcyclopentadienyl Rhodium Complexes in Catalytic C-H Annulations. Application for Synthesis of Natural Isocoumarins

Efficient protocols for the synthesis of triphenylcyclopentadienyl rhodium halides [(1,2,4-C₅Ph₃H₂)RhX₂]₂ (1a,b: X = Cl, I) starting from 1,2,4-triphenylcyclopentadiene or the cyclooctadiene derivative (1,2,4-C₅Ph₃H₂)Rh(cod) (2) were developed. Iodide abstraction from 1b with thallium or silver salts allowed us to prepare rhodocenium [(1,2,4-C₅Ph₃H₂)RhCp]PF₆ (3PF₆) and mesitylene complex [(1,2,4-C₅Ph₃H₂)Rh(mesitylene)](SbF₆)₂ (4(SbF₆)₂). Halides 1a,b (at 0.5 mol % loading) showed high catalytic activity in the construction of C-C, C-O, and C-N bonds via the C(sp²)-H activation approach. Their efficiency was demonstrated in the synthesis of more than 40 examples of polycyclic organic compounds (such as isocoumarins and naphthalenes, as well as isoquinolinium and dibenzo[a,f]quinolizinium salts). The protocols developed tolerate a wide range of functional groups. In particular, they were successfully used for the atom- and step-economical synthesis of hydroxy-substituted isocoumarins, including the natural product oospalactone 7fe. The 6- or 8-hydroxy-substituted isocoumarins showed moderate antiproliferative activity against several human cell lines in vitro.

New Aspects of Ruthenium-Mediated Polyhedral Contraction of Monocarbollides

It has been shown that the interaction of tris(triphenylphosphine)ruthenium dichloride RuCl2(PPh3)3 (1) with 10-vertex monocarborane [6-Ph-nido-6-CB9H11]−[Et4N]+ (2) under mild thermolysis conditions is not selective due to the undesired coordination of ruthenium to a phenyl substituent in the carborane and phosphine ligands, giving the series of new classical and non-classical metallacarborane complexes. In contrast, the reaction of 1 and monocarborane [arachno-6-CB9H14]−[Et4N]+ (3) proceeds more selectively with the formation of the only one product, a isocloso-structured metallacarborane. The structures of two ruthenacarboranes were resolved by X-ray diffraction.